Nodes are data structures which constitute a binary space partition of a map. They are generated by nodebuilders, and they make up a binary tree that sorts all the subsectors into the correct order for drawing. Each node entry has a partition line associated with it that divides the area that the node represents into a left child area and a right child area. Each child may be either another node entry (a subnode), or a subsector on the map.
Each of the two bounding boxes describe a rectangle which is the area covered by each of the two child nodes respectively. A bounding box consists of four short values (top, bottom, left and right) giving the upper and lower bounds of the y coordinate and the lower and upper bounds of the x coordinate (in that order).
The type of each child field is determined by its sign bit (bit 15). If bit 15 is zero, the child field gives the node number of a subnode. If bit 15 is set, then bits 0-14 give the number of a subsector.
NODES is the resource lump containing the list of nodes for a map, with the root node of the map listed last.